1. Field of the Invention
The present invention relates to a suspension arm of a vehicle, and more particularly to an A-shaped suspension arm made of fiber reinforced plastic, the suspension arm being provided between a vehicle body and a wheel.
2. Description of the Related Art
An upper arm, as a suspension arm, made of fiber reinforced plastic (FRP) is described in the TOYOTA Technical Report, April, 1989. This upper arm is adapted to connect a ball joint comprising a wheel-side connecting member connected to a wheel to a rubber bush comprising a vehicle-side connecting member connected to a vehicle body.
The above-mentioned FRP upper arm has an increased rigidity in a side direction of a vehicle without increased rigidity in a longitudinal direction of the vehicle, and thereby riding comfort and stability and controllability of the vehicle are improved. The FRP upper arm has a flat A-shaped contour so as to obtain a high strength against a load applied in the longitudinal direction. Additionally, the FRP upper arm has three different patterns of fibers incorporated therein, the fibers being wound on the ball joint, run through an arm portion and then wound on a bush portion.
However, since the above-mentioned FRP upper arm is made to be a rigid member, there is no flexibility in the longitudinal direction of the vehicle. Accordingly, in order to absorb the load applied in the longitudinal direction, a rubber bush having an elasticity has to be provided on each end of the FRP arm. The rubber bush is required to show a predetermined elastic property even after a long service time.
Additionally, because the FRP upper arm has the A-shaped contour, tensile and compression stresses due to the load applied in the longitudinal direction increase at portions of the FRP upper arm near the ball joint and the rubber bush. In order to deal with these stresses, rigidity of an entire arm has to be increased, and thus a weight of the arm is increased resulting in an increase in material costs.
A further problem is that construction of the rubber bush is complex and expensive because the rubber bush has to absorb the load in the longitudinal direction so as to provide riding comfort to the vehicle.